The invention relates to a method as recited in the preamble of claim 1. Maximum Likelihood Sequence Estimation is a powerful signal detection tool and can be theoretically proved to give optimum detection both for linear and for non-linear systems.
In high-density optical recording, because of high linear density and reduced track pitch, the signal read-out is not a linear process anymore. A linear process will then impose an upper limit on storage density and therefore a non-linear approach should be taken. MLSE, although optimal, is not a reasonably straightforward and efficient implementation because of its computational complexity. The inventors, on the basis of a study carried out on a Volterra model of the non-linear optical channel drawn by the Hopkins analysis, have taken an improved approach. In fact, they have recognized that first and second orders of signal distortion are mutually uncorrelated. This has led to an innovated read-out processing, wherein linear and non-linear distortions are treated separately, while still using the MLSE structure that may be simplified dramatically.The Non-linear MLSE is based on a two-stage structure that performs linear as well as non-linear processing. The first stage has an adaptive matched filter and a non-linear Volterra canceller for preprocessing the signal to remove its non-linear distortion coefficient. The remainder signal is now only affected by linear distortion, and processed in the usual manner in an MLSE based on a Viterbi detector (VD).
In consequence, amongst other things, it is an object of the present invention to combine linear and non-linear detection mechanisms into an innovative linear and non-linear receiver structure. Now therefore, according to one of its aspects the invention is characterized according to the characterizing part of claim 1.
The invention also relates to a device arranged for implementing the above method. Further advantageous aspects of the invention are recited in dependent Claims.